1. Field of the Invention
The present invention is utilized as a steplessly variable transmission in which a wrapping transmission includes an endless chain.
2. Description of the Prior Art
Generally, a friction gearing chain drive, as illustrated by FIG. 1, comprises a driving shaft D and a driven shaft F spaced from one another and each being equipped with a pair of transmission sheaves Pl, Pl and P2, P2, respectively, each having opposing cone surfaces. Such drive is utilized for gear ratio changes by expanding or contracting the facing gaps of the transmission sheaves P1, P1 and P2, P2 so that contacting positions between a plurality of friction gearing members B assembled with an endlessly wrapped transmission chain C disposed between both sheaves and the opposing cone surfaces of the transmission sheaves can be changed in response to the shifting of the transmission sheaves. The friction gearing chain is roughly classified into two types in accordance with the shape of the pins which endlessly connect a plurality of link plates constituting the transmission chain C; that is, a rocker-pin type and a round-pin type, and the rocker-pin type is adopted mainly for a silent chain. The present invention relates to a rocker-pin type friction gearing chain. A conventional rocker-pin type friction gearing chain is, as shown in Laid-open Japanese Patent Application No. 59-99142 (1984), and in corresponding U.S. Pat. No. 4,507,106, formed in such a manner that a traction load transmitting surface, at which a rocker pin and an insertion hole for the rocker pin as formed in a link plate contact and engage each other, is formed by a continuous surface which is made by continuously connecting a plurality of arc-shaped surfaces having different curvatures. It is the aim of this arrangement to prevent a mutual rotational displacement between the rocker pin and the link plate. However, as explained in the above-mentioned application No. 59-99142, it is extremely difficult to manufacture a plurality of arcshaped surfaces having different curvatures so as to contact and engage at all surfaces.
In view of this, in order to eliminate such difficulty, the arrangement disclosed in U.S. Pat. No. 4,801,289, as owned by the assignee hereof, has been invented.
That is, aforementioned U.S. Pat. No. 4,801,289 shows, as shown in FIG. 3 hereof, that a rocker pin P has a plane portion 1 formed by removing a central portion of a traction load transmitting surface of the rocker pin and a pair of arc-shaped convex surfaces 2, 2 each continuously connected to respective ends of the plane portion 1 and formed concentric about a common axis. To the contrary, the insertion hole H is formed to include a concave curved surface 3 which faces but does not contact the plane portion 1, and further includes arc-shaped concave surfaces 4, 4 continuously connected to opposite ends of the concave curved surface 3. The arc-shaped concave surfaces 4, 4 engagedly contact with the pair of arc-shaped convex surfaces 2, 2 so that the arc-shaped convex surfaces 2, 2 and the arcshaped concave surfaces 4, 4 form the traction load transmitting surface. The concave curved surface 3 and the arc-shaped concave surfaces 4, 4 have different curvatures.
Accordingly, the mutual rotational displacement between the rocker pin and the link plate is restricted in such a way that inflection points 5 between the plane portion 1 of the rocker pin and the arc-shaped convex surfaces 2, 2 is engaged with inflection points 6 between the concave curved surface 3 and the arc-shaped concave surfaces 4, 4.
As explained above, and in accordance with the technical content disclosed in U.S. Pat. No. 4,801,289, the arc-shaped convex surfaces 2, 2 and the arc-shaped concave surfaces 4, 4 are formed to be concentric arc-shaped surfaces. Therefore it becomes possible to resolve the technical problem disclosed in Laid-open Japanese Patent Application 59-99142 in view of easiness in manufacturing so as to be able to engagedly contact. However, since the arc-shaped convex surfaces 2, 2 and the arc-shaped concave surfaces 4, 4 are formed to be concentric arc-shaped surfaces, a restriction force for preventing mutual rotational displacement is not expected because the engaged contacting surface is of a freely rotatable type. Therefore a load caused for counteracting the mutual rotational displacement concentrates on an engaging portion at the inflection points 5 and the inflection points 6. Thus, a crack is generated from this engaging point of the inflection points 5 and 6, and it is feared that this crack in turn may cause a breakage of the link plate.